Dear sir/ma, I’m fifty years old ever since I’ve never got a visa non travel abroad to any country, so can I apply for your US Visa for the first time and be granted? Expect your urgent reply please. Thanks

Your age does not determine if you would be given or denied visa.
As long as you have a genuine reason for visiting a country like an employment from a company in that country, schooling with evidence you can fund it, you have strong ties to Nigeria which would make you come back and you can comfortably sponsor yourself.
Then you are certain to be given a visa.
Most rejection happens if there is no genuine reason and one is suspected not to come back to Nigeria once that person gets there.